In 3GPP (3rd Generation Partnership Project) that is a standardization project, standardization of an OFDM (Orthogonal Frequency-Division Multiplexing) communication mode, or Evolved Universal Terrestrial Radio Access (hereinafter, referred to as “EUTRA”) that realizes high-speed communication by employing flexible scheduling at a predetermined frequency unit and time unit called a resource block has been carried out.
In addition, in the 3GPP, advanced EUTRA which realizes further high-speed data transmission and has upper compatibility with EUTRA has been discussed. As a technique in advanced EUTRA, carrier aggregation (CA) has been suggested. The carrier aggregation is a technique of improving a transmission rate by using a plurality of different frequencies (component carriers, also referred to as CC) in an aggregated manner. In addition, there is suggested a technique in which a mobile-station apparatus in communication with a base-station apparatus by using the carrier aggregation has a plurality of uplink transmission timings (Timing Advance; TA) for each frequency or component carrier (NPL 1).
In EUTRA, a random access procedure is prepared to adjust the uplink transmission timing of the mobile-station apparatus. With regard to the random access procedure, a method, in which the base-station apparatus configures information indicating initiation of the random access procedure to a physical downlink control channel and transmits the information in order for a specific mobile-station apparatus to initiate the random access procedure, may be exemplified in addition to a method in which the mobile-station apparatus autonomously determines necessity of the random access procedure and initiates the random access procedure.
In addition, in the 3GPP, in a case where the mobile-station apparatus in communication with the base-station apparatus by using the carrier aggregation needs a different uplink transmission timing for each frequency or a plurality of frequencies (component carriers), there are suggested that frequencies (component carriers) of the same uplink transmission timing are grouped, and a timer (transmission timing timer, Timing Alignment Timer; TAT) that manages a state of the uplink transmission timing is provided for each group, or that one reference cell that is used as a reference of the uplink transmission timing is provided for each group (NPL 2). In addition, a group in which the uplink transmission timings indicate the same frequency (component carrier) is also referred to as a transmission timing group (Timing Alignment Group; TAG).
In 3GPP, there is also suggested that a group, to which the frequency (component carrier) of the mobile-station apparatus in communication with the base-station apparatus by using the carrier aggregation belongs, can be changed to another group for each frequency (component carrier) by instruction from the base-station apparatus (NPL 3).
In addition, the base-station apparatus constitutes one cell by combining one downlink component carrier and one uplink component carrier. In addition, the base-station apparatus may constitute one cell by only one downlink component carrier.